The present invention claims priority from Japanese Patent Application No. 10-254202 filed Sep. 8, 1998, the contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an actuator of an ink jet recording head, for recording characters and/or pictures by jetting ink droplets to a recording medium such as a recording sheet.
2. Description of Related Art
FIG. 9 is a cross section of an actuator of a conventional ink jet recording head, showing a structure of a main portion of the actuator. This structure has a purpose of illustrating a structure of one of pressure chambers of the ink jet recording head and one of ink nozzles thereof. In this conventional structure, a space defined by nozzle plate 31 formed of a rigid material and casing 34 formed of a rigid material is used as pressure chamber 33, which is filled with externally supplied ink 5. Nozzle 32 for jetting ink droplet 1 is formed in nozzle plate 31 and drive plate 35 is provided within pressure chamber 33. Drive plate 35 is formed of a piezoelectric material (or a material having large thermal expansion coefficient) and has opposite surfaces, on which electrodes 39 are formed, respectively. When a voltage is applied across electrodes 39 from power source 40 through switch 37 as an electric signal, drive plate 35 is deformed in a direction shown by, for example, an arrow by the piezoelectric effect (or thermal expansion) as shown, to pressurize ink 5 filling pressure chamber 33 to thereby jet ink droplet 1 out through nozzle 32.
In this conventional structure, drive plate 35 is put on support portion 38 and adhered thereto as shown in FIG. 10 (Japanese Patent Application Laid-open No. Hei 9-85946). That is, in order to control the direction of deformation constant, one of the surfaces of drive plate 35 is fixed by adhesive to support portion 38, by which displacement thereof is restricted. Therefore, a compressive reactive force is exerted on a portion between drive plate 35 and support portion 38 as shown by horizontal inward arrows in FIG. 10, every time when the pressure chamber is driven.
That is, since, when the actuator having such structure is driven, a reactive force of the driving force is repetitively exerted on the adhesive layer between driving plate 35 and support portion 38, shearing deformation tends to occur in the adhesive layer. When such shearing deformation occurs in the adhesive layer, displacement in a direction parallel to the plane of driving plate 35 is relieved thereby and, therefore, an amount of displacement of driving plate 35 in a direction shown by a thick arrow in FIG. 10 becomes small. If such shearing deformation is considerable, driving plate 35 may be peeled off from support portions 38 by the reactive force of the driving force. In the latter case, a driving force for pressurizing ink pressure chamber 33 may not be produced at all. That is, this phenomenon may cause the life of the ink jet recording head to be shortened. Further, in such structure of the actuator, an adhering step is required in a manufacture thereof. In such adhering step, a precise positioning is necessary, with which the number of manufacturing steps may be increased. Further, since a positioning error, a variation of adhering strength and a variation of thickness of the adhering layer, etc., are reflected on a variation of the ink jet characteristics, that is, printing characteristics, manufacturing yield of the ink jet recorder may be lowered.
The present invention was made in view of the above mentioned fact and has an object to provide an ink jet recording head whose ink jetting characteristics is not influenced directly by a positioning error, a variation of adhering strength and a variation of thickness of an adhesive layer, etc., thereof which may be caused by the necessity of adhesion of a driving plate to the support portion.
Another object of the present invention is to provide an ink jet recording head capable of being manufactured without using the adhering step for adhering a driving plate to a support portion.
Another object of the present invention is to provide an ink jet recording head capable of substantially increasing the number of effective reciprocal movements of the driving plate to thereby allow a life thereof to be lengthened.
A further object of the present invention is to provide an ink jet recording head which rarely breaks down and is highly reliable.
Another object of the present invention is to provide an ink jet recording head whose variation of performance over time is minimized.
Another object of the present invention is to provide an ink jet recording head capable of being manufactured with a small number of manufacturing steps.
A still further object of the present invention is to provide an ink jet recording head with which an ink jet recorder having a uniform performance can be manufactured.
Another object of the present invention is to provide an ink jet recording head which can be manufactured with high yield.
In order to achieve the above objects, the ink jet recording head according to the present invention, which has a structure in which an ink chamber is pressurized by utilizing a buckling deformation of a driving plate, is featured by that a pressuring unit has a structure in which an adhesive layer is not influenced by displacement caused by every pressurization of the ink chamber.
That is, in an ink jet recording head including a rigid member defining a pressure chamber formed with a nozzle for jetting ink droplet and a pressuring unit for pressurizing ink filling the pressure chamber correspondingly to an electric signal, the present invention is featured by that the pressurizing unit comprises at least one beam supported at opposite end portions thereof and a support portion for supporting the opposite end portions of the beam and restricting an expansion of the beam in its longitudinal direction such that, when the beam is expanded in the longitudinal direction due to an application of the electric signal, the expanded portion of the beam is buckled into the pressure chamber.
The beam is made of a piezo-electric material. At least one electrode for applying an electric signal is formed on a surface of the beam. Alternatively, the beam may be made of a material having large thermal expansion coefficient and a heater for heating the beam upon an application of the electric signal may be provided. The beam and the support portion are preferably formed integrally. The beam and the support portion may be integrally formed from a piezo-electric material sheet by punching and the electrode is formed on the beam.
A recess for controlling a direction of buckling deformation of the beam is formed in the beam. It is possible to form such recess at a position deviated in the longitudinal direction of the beam from a center of the beam or it is possible to provide an electrode for controlling the direction of buckling deformation of the beam on the latter partially.
The pressurizing unit pressurizes ink in the pressure chamber having the nozzle for jetting ink droplet in response to the electric signal. The pressurization is performed by applying the electric signal to the beam formed continuously to the support portion for restricting the expansion of the beam in its longitudinal direction to expand the beam in the same direction to thereby buckle the beam into the pressure chamber. By this buckling deformation of the beam, ink in the pressure chamber is pressurized and jetted through the nozzle as ink droplet.
In order to realize the buckling deformation of the beam, the beam may be formed of a piezo-electric material and an electric signal is applied to an electrode provided on a surface of the beam. When the electric signal is applied to the electrode, the beam is expanded in its longitudinal direction, buckled toward the pressure chamber and pressurizes the pressure chamber.
Alternatively, the beam may be formed of a material having large thermal expansion coefficient and it is possible to form the beam of a material having large thermal expansion coefficient and, by applying the electric signal to a heater provided on a surface of the beam to heat the beam to pressurizing the ink chamber.
By integrally constructing the beam having the buckling structure and the support portion supporting the opposite end portions of the beam, there is no need of receiving a reactive force against a shearing force produced between the opposite end portions of the beam and the support portion by an adhesive layer when a buckling deformation occurs, so that it is possible to realize the buckling deformation effectively. Incidentally, the buckling deformation is realized within the elastic limit of the beam.
The integral structure of the beam and the support portion can be easily realized by cutting it out from a plate of piezo-electric material and the pressurizing part can be manufactured by merely providing an electrode on the thus formed beam.
The buckling deformation of the beam must be in the direction toward the pressure chamber filled with ink. In order to make the direction of buckling deformation constant, a recess is formed in a surface of the beam on the side opposite to the direction. With such recess, it becomes possible to buckle the beam in the direction constantly when the electric signal is applied to the electrode or the heater provided on the beam. Further, it is possible to set an amount of buckling deformation required for the pressurizing unit by changing the depth of the recess.
The position of the recess in the beam is not always a center of the beam in its longitudinal direction and the recess can be formed at a position deviated from the center. In the latter case, the length of the electrode formed on one side of the beam becomes different from that of the electrode formed on the other side of the beam. The amount of buckling deformation of the beam when the electric signal is applied to the shorter electrode is different from that when the electric signal is applied to the longer electrode and the amount of buckling deformation of the beam when the electric signal is applied to both the shorter and longer electrodes is also different from those when the electric signal is applied to the shorter or longer electrode. Therefore, with the structure of the present invention, it is possible to control the amount of ink to be jetted by selecting the electrode to which the electric signal is to be applied. Consequently, it becomes possible to jet an amount of ink required for a printing by controlling the application of the electric signal to the respective electrodes.
When the electrode is partially embedded in the beam, an axis of action of buckling deformation when the electric signal applied thereto becomes eccentric with respect to the axis of the beam. Therefore, in such case, it is possible to maintain the direction of buckling deformation of the beam constant even without the recess.
As mentioned, according to the present invention, the pressurizing unit can be formed by the beam and the support portion for supporting the beam at opposite end portions thereof, which are formed integrally. Therefore, there is no need of adhering the driving plate to the support member thereof and a reactive force for a force exerted on the beam in the longitudinal direction thereof is not exerted on the adhesive layer, contrary to the conventional ink jet recording head. Therefore, the positioning error, the variation of adhering strength and the variation of thickness of the adhesive layer, etc., do not influence the ink jetting characteristics of the ink jet recording head.
Further, since there is no reactive force exerted on the adhering portion of the constitutional members, the number of effective reciprocal drives of the vibration plate is increased and a change of performance of the ink jet recording head with time can be reduced. Therefore, a reduction of the life of the ink jet recording head due to occurrences such as the peeling-off of the adhesive layer can be avoided, thereby improving the reliability of the ink jet recording head.
Further, it is possible to manufacture the ink jet recorder having uniform performance with minimum number of manufacturing steps and to simplify the manufacturing work. Further, it is possible to make the quality of the ink jet recording head uniform and to improve the yield thereof.